A 3-month-old boy presents in winter with a 2-day history of coryzal symptoms, poor feeding and increasing work of breathing. On examination, he has tachypnoea, subcostal recession, widespread fine crackles and wheeze, and oxygen saturations of 92% in air. He is feeding poorly but is haemodynamically stable. According to Australasian bronchiolitis guidance, what is the mainstay of management?